The detection of a signal sequence of a constant phase change at each sampling time interval included in a demodulated signal in accordance with the synchronous detection of a received signal is conventionally carried out.
In a time division multiple access (TDMA) communication system in which transmitting and received signals are at burst state in a multiple transmission line, a synchronism detection signal composed of a particular signal sequence is included in a transmitting signal along with transmitting data, so that a transmitted signal of a burst type can be received in a receiving circuit at each station in which the arrival of the transmitted signal is acknowledged by detecting the synchronism detection signal, and the transmitted data included in the received signal is demodulated. In general, the demodulated signal obtained by demodulating the received signal is defined as a signal vector, because it includes an in-phase component (I channel signal) and a vertical component (Q channel signal).
In conventionally detecting a particular signal sequence included in a received signal, the phase of a signal vector obtained by synchronously detecting the received signal is sampled by a sampling rate equal to a symbol rate, so that a particular signal sequence is detected by detecting a phase difference between first and second phase values having a predetermined value, wherein the second phase value obtained at a selected symbol time and the first phase value obtained at a symbol time prior to the selected symbol time by one symbol are compared in a limited number of consecutive symbols.
However, there is a disadvantage in the conventional method for detecting a particular signal sequence in that noise is added to the transmission line resulting in errors in the ideal phase. This tends to make it impossible for a particular signal sequence to be detected.